The present invention generally relates to a picture image distributing apparatus provided within a passenger moving vehicle for distributing multichannel picture image signals to the respective passenger seats within the passenger moving vehicle.
The conventional picture image distributing apparatus provided within a passenger moving vehicle is one using the same coaxial cables as in, for example, CATV. The distributing operation of the signals is effected by the taking out operation of the signals where necessary by a tapping system from the coaxial cable.
A network construction of distributing optical signals using fiber optics generally uses topology of a star type using an optical branching unit of such equal distribution as shown in FIG. 9 (A), of a double star type or of a multistage star type as in FIG. 9 (B). This is because the loss of the whole network which becomes a problem in an optical signal distribution system can be reduced as much as possible since the optical branching unit having an equal distribution has the least losses. Therefore, the number of all distributions can be maximized.
As to the prior art disclosing a signal distribution using fiber optics, there is, for instance, a paper entitled "OPTICAL AMPLIFIERS FOR VIDEO DISTRIBUTION" written by D. R. HUBER and J. B. GLAAB, and published in the INTERNATIONAL JOURNAL 0F DIGITAL AND ANALOG COMMUNICATION SYSTEMS, VOL. 3, pp. 333-339, (1990).
In a picture image distributing apparatus provided within a passenger moving vehicle using a tapping system using coaxial cables as in the above description, electromagnetic interference is not only easily received from the electromagnetic environment interior within the passenger moving vehicle, but also easily generates electromagnetic interference with respect to the other equipment, with a problem in that the influences upon the signals by differences and variations in the electrical ground potential are unavoidable.
In order to avoid such electromagnetic problems, fiber optics are used as a transmission path. In the network construction of a star type or a multistage star type, the number of core wires of the optical fibers to be laid in the longitudinal direction is increased within a passenger moving vehicle of narrow construction such as an airplane or train, and especially becomes greater near the head end portion. Generally, the passenger moving vehicle of a narrow construction such as an airplane and train has narrow conduit lines therein for the transmission path use or in the space for them, with a problem in that the optical fibers of many core wires must be laid. Weight increases, and the wiring becomes complicated. There is a problem in that it takes more time to detect the locations of the breaks in the optical fibers. Although the optical fibers must be connected with the optical connectors so as to be disengaged from the transmission path for maintenance, the number of optical connectors become very large, and the space needed for them becomes larger. The maintenance and repair steps increase in number. When the optical fibers are to be connected again after the disconnection thereof, a problem arises in that the discrimination between the optical fibers is difficult.